          (pmap
           (fn [[l ls]]
             (let [node-times (map (comp c/to-long :ts) ls)]
-              (if (empty? node-times)
+              (if (< (count node-times) 2)
                 nil
                 (/ (->> (t/interval
                          (c/from-long (apply min node-times))

                (pmap
                 (fn [[l ls]]
                   (let [node-times (map (comp c/to-long :ts) ls)]
                     (if (empty? node-times)
                       nil
                       (/ (->> (t/interval
                              (c/from-long (apply min node-times))
                              (c/from-long (apply max node-times)))
                             t/in-seconds)
                          3600)))))
                (remove nil?)
                statistics)))

         (pmap
          (fn [[l ls]]
            (let [node-times (map (comp c/to-long :ts) ls)]
              (if (< (count node-times) 2)
                nil
                (/ (->> (t/interval
                         (c/from-long (apply min node-times))
